Gated semiconductor assemblies and methods of forming gated semiconductor assemblies

ABSTRACT

In one aspect, the invention includes a method of forming a gated semiconductor assembly, comprising: a) forming a silicon nitride layer over and against a floating gate; and b) forming a control gate over the silicon nitride layer. In another aspect, the invention includes a method of forming a gated semiconductor assembly, comprising: a) forming a floating gate layer over a substrate; b) forming a silicon nitride layer over the floating gate layer, the silicon nitride layer comprising a first portion and a second portion elevationally displaced from the first portion, the first portion having a greater stoichiometric amount of silicon than the second portion; and c) forming a control gate over the silicon nitride layer. In yet another aspect, the invention includes a gated semiconductor assembly comprising: a) a substrate; b) a floating gate over the substrate; c) a control gate over the floating gate; and d) an electron barrier layer between the floating gate and the control gate, the electron barrier layer comprising a silicon nitride layer, the silicon nitride layer comprising a first portion and a second portion elevationally displaced from the first portion, the first portion having a greater stoichiometric amount of silicon than the second portion.

TECHNICAL FIELD

[0001] The invention pertains to gated semiconductor assemblies, suchas, for example, erasable, programmable read-only memories (EPROMS),electrically erasable proms (EEPROMS), and flash EEPROMS.

BACKGROUND OF THE INVENTION

[0002] Read-only-memories (ROMs) are memories into which information ispermanently stored during fabrication. Such memories are considered“non-volatile” as only read operations can be performed.

[0003] Each bit of information in a ROM is stored by the presence orabsence of a data path from the word (access) line to a bit (sense)line. The data path is eliminated simply by insuring no circuit elementjoins a word and bit line. Thus, when the word line of a ROM isactivated, the presence of a signal on the bit line will mean that a 1is stored, whereas the absence of a signal indicates that a 0 is stored.

[0004] If only a small number of ROM circuits are needed for a specificapplication, custom mask fabrication might be too expensive or timeconsuming. In such cases, it would be faster and cheaper for users toprogram each ROM chip individually. ROMs with such capabilities arereferred to as programmable read-only-memories (PROMs). In the firstPROMs which were developed, information could only be programmed onceinto the construction and then could not be erased. In such PROMs, adata path exists between every word and bit line at the completion ofthe chip manufacture. This corresponds to a stored 1 in every dataposition. Storage cells during fabrication were selectively altered tostore a 0 following manufacture by electrically severing the word-to-bitconnection paths. Since the write operation was destructive, once the 0had been programmed into a bit location it could not be erased back toa 1. PROMs were initially implemented in bipolar technology, althoughMOS PROMs became available.

[0005] Later work with PROMs led to development of erasable PROMs.Erasable PROMs depend on the long-term retention of electric charge asthe means for information storage. Such charge is stored on a MOS devicereferred to as a floating polysilicon gate. Such a construction differsslightly from a conventional MOS transistor gate. The conventional MOStransistor gate of a memory cell employs a continuous polysilicon wordline connected among several MOS transistors which functions as therespective transistor gates. The floating polysilicon gate of anerasable PROM interposes a localized secondary polysilicon gate inbetween the continuous word line and silicon substrate into which theactive areas of the MOS transistors are formed. The floating gate islocalized in that the floating gates for respective MOS transistors areelectrically isolated from the floating gates of other MOS transistors.

[0006] Various mechanisms have been implemented to transfer and removecharge from a floating gate. One type of erasable programmable memory isthe so-called electrically programmable ROM (EPROM). The charge-transfermechanism occurs by the injection of electrons into the floatingpolysilicon gate of selected transistors. If a sufficiently highreverse-bias voltage is applied to the transistor drain beingprogrammed, the drain-substrate “pn” junction will experience“avalanche” breakdown, causing hot electrons to be generated. Some ofthese will have enough energy to pass over the insulating oxide materialsurrounding each floating gate and thereby charge the floating gate.These EPROM devices are thus called floating-gate, avalanche-injectionMOS transistors (FAMOS). Once these electrons are transferred to thefloating gate, they are trapped there. The potential-barrier at theoxide-silicon interface of the gate is greater than 3 eV, making therate of spontaneous emission of the electrons from the oxide over thebarrier negligibly small. Accordingly, the electronic charge stored onthe floating gate can be retained for many years.

[0007] When the floating gate is charged with a sufficient number ofelectrons, channel function is inhibited. The presence of a 1 or 0 ineach bit location is therefore determined by the presence or absence ofa conducting floating channel gate in each program device.

[0008] Such a construction also enables means for removing the storedelectrons from the floating gate, thereby making the PROM erasable. Thisis accomplished by flood exposure of the EPROM with strong ultravioletlight for approximately 20 minutes. The ultraviolet light createselectron-hole pairs in the silicon dioxide, providing a discharge pathfor the charge (electrons) from the floating gates.

[0009] In some applications, it is desirable to erase the contents of aROM electrically, rather than to use an ultraviolet light source. Inother circumstances, it would be desirable to be able to change one bitat a time, without having to erase the entire integrated circuit. Suchled to the development of electrically erasable PROMs (EEPROMs). Suchtechnologies include MNOS transistors, floating-gate tunnel oxide MOStransistors (FLOTOX), textured high-polysilicon floating-gate MOStransistors, and flash EEPROMs. Such technologies can include acombination of floating gate transistor memory cells within an array ofsuch cells, and a peripheral area to the array which comprises CMOStransistors.

[0010] A prior art EPROM device is described with reference tosemiconductor wafer fragment 10 of FIGS. 1-3. FIG. 1 is a top view ofwafer fragment 10, and FIGS. 2 and 3 are cross-sectional side viewsalong the lines labelled X-X and Y-Y, respectively, in FIG. 1. Waferfragment 10 comprises a substrate 12, having field oxide regions 14formed thereover. Substrate 12 can comprise, for example, lightly dopedmonocrystalline silicon. To aid in interpretation of the claims thatfollow, the term “semiconductive substrate” is defined to mean anyconstruction comprising semiconductive material, including, but notlimited to, bulk semiconductive materials such as a semiconductive wafer(either alone or in assemblies comprising other materials thereon), andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term “substrate” refers to any supportingstructure, including, but not limited to, the semiconductive substratesdescribed above.

[0011] Field oxide regions 14 can comprise, for example, silicondioxide. An active region 15 extends over and within substrate 12between field oxide regions 14. A floating gate 16 and a control gate 18are formed over the active region. Gates 16 and 18 can comprise, forexample, conductively doped polysilicon.

[0012] Floating gate 16 is separated from substrate 12 by a tunnel oxide11 layer 20. Gates 16 and 18 are separated from one another by aninsulative layer 22 which can comprise, for example, a combination ofsilicon dioxide and silicon nitride, such as the shown ONO constructionwherein a silicon nitride layer 17 is sandwiched between a pair ofsilicon dioxide layers 19. The silicon nitride comprises Si₃N₄, althoughother forms of silicon nitride are known. Such other forms includesilicon enriched silicon nitride layers (i.e., silicon nitride layershaving a greater concentration of silicon than Si₃N₄, such as, forexample, Si₄N₄). An advantage of silicon-enriched silicon nitride layersrelative to Si₃N₄ is that the silicon-enriched silicon nitride layersfrequently do not require separate, discrete antireflective coatingsformed between them and a photoresist. However, silicon enriched siliconnitride is difficult to pattern due to a resistance of the material toetching. Silicon enriched silicon nitride layers are formed to have asubstantially homogenous composition throughout their thicknesses,although occasionally a small portion of a layer (1% or less of athickness of the layer) is less enriched with silicon than the remainderof the layer due to inherent deposition problems.

[0013] Wafer fragment 10 further comprises silicon dioxide layers 24 and26 extending along sidewalls of gates 16 and 18, and comprises a silicondioxide layer 28 over control gate 18. Layers 24, 26 and 28 canelectrically insulate gates 16 and 18 from other circuitry (not shown)that may be present on substrate 12.

[0014] The gate assembly shown in FIGS. 1-3 can be formed as follows.Initially, a portion of substrate 12 within the active region isoxidized to form an oxide layer which will ultimately be patterned intotunnel oxide 20. Next, a polysilicon layer is formed over the silicondioxide layer, with the polysilicon layer ultimately being patterned toform floating gate 16. An antireflective coating is formed over thepolysilicon layer, and a layer of photoresist formed over theantireflective coating.

[0015] After the photoresist is formed, it is patterned by selectivelyexposing portions of the photoresist to light to render the portionseither more soluble or less soluble in a solvent than portions which arenot exposed to the light. The antireflective coating absorbs light thatpenetrates the photoresist to prevent such light from reflecting back toeither constructively or destructively interfere with other lightpassing through the photoresist. The photoresist is then exposed to thesolvent to remove the more soluble portions of the photoresist and leavea patterned photoresist block over a portion of the polysilicon layerthat is to become floating gate 16.

[0016] The patterned photoresist block protects the portion of thepolysilicon layer it covers, while uncovered portions of theantireflective coating, polysilicon layer, and silicon oxide layers areremoved with an etch. The portions of the polysilicon layer and oxidelayer which remain are in the shape of floating gate 16 and tunnel oxide20.

[0017] After the etch of the antireflective coating, polysilicon andoxide, the photoresist and antireflective coating are removed from overfloating gate 16. The polysilicon of floating gate 16 is then exposed tooxygen under conditions which form a silicon dioxide layer over exposedsurfaces of the polysilicon to create oxidized sidewalls 24 and 26, anda portion of insulative layer 22. Subsequently, layers of siliconnitride and silicon dioxide are provided to complete formation ofinsulative layer 22. Next, a second polysilicon layer is provided andpatterned to form control gate 18. The second polysilicon layer is thenexposed to oxygen to form silicon dioxide layers 24 and 26 at thesidewalls of control gate 18, and to form silicon dioxide layer 28 overa top of control gate 18.

[0018] Source and drain regions can be provided within active area 15and operatively adjacent floating gate 16. The source and drain regionscan be provided by implanting a conductivity enhancing dopant intosubstrate 12 after forming floating gate 16 and before oxidizingsidewalls of floating gate 16.

[0019] A continuing goal in semiconductor device fabrication is tominimize the number of fabrication steps required to form asemiconductor device. Accordingly, it would be desired to eliminate oneor more of the above-discussed steps in forming a gated semiconductorassembly.

SUMMARY OF THE INVENTION

[0020] In one aspect, the invention encompasses a method of forming agated semiconductor assembly. A silicon nitride layer is formed over andagainst a floating gate. A control gate is formed over the siliconnitride layer.

[0021] In another aspect, the invention encompasses a method of forminga semiconductor assembly. A first material layer is formed over asubstrate. A silicon nitride layer is formed over the first materiallayer. The silicon nitride layer comprises a first portion and a secondportion elevationally displaced from the first portion. The firstportion has a greater stoichiometric amount of silicon than the secondportion. A photoresist layer is formed over the first material layer andthe silicon nitride layer. The photoresist layer is patterned. Thepatterning comprises exposing portions of the layer of photoresist tolight and utilizing the silicon nitride layer as an antireflectivesurface during the exposing. The pattern is transferred from thepatterned photoresist to the silicon nitride layer and the firstmaterial layer.

[0022] In yet another aspect, the invention encompasses a gatedsemiconductor assembly comprising a substrate, a floating gate over thesubstrate, a control gate over the floating gate, and an electronbarrier layer between the floating gate and the control gate. Theelectron barrier layer comprises a silicon nitride layer. The siliconnitride layer comprises a first portion and a second portionelevationally displaced from the first portion. The first portion has agreater stoichiometric amount of silicon than the second portion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

[0024]FIG. 1 is a fragmentary, diagrammatic top view of a prior artgated semiconductor assembly

[0025]FIG. 2 is a diagrammatic, fragmentary, cross-sectional view of theFIG. 1 gated semiconductor assembly along the line X-X of FIG. 1.

[0026]FIG. 3 is a diagrammatic, fragmentary, cross-sectional view of theFIG. 1 gated semiconductor assembly along the line Y-Y of FIG. 1.

[0027]FIG. 4 is a diagrammatic, fragmentary, cross-sectional view of asemiconductor wafer fragment at a preliminary processing step of amethod of the present invention, shown along an axis corresponding toline X-X of FIG. 1.

[0028]FIG. 5 is a view of the FIG. 4 wafer fragment shown along an axiscorresponding to line Y-Y of FIG. 1.

[0029]FIG. 6 is a view of the FIG. 4 wafer fragment shown at aprocessing step subsequent to that of FIG. 4, and shown along an axiscorresponding to line X-X of FIG. 1.

[0030]FIG. 7 is a view of the FIG. 6 wafer fragment shown along an axiscorresponding to line Y-Y of FIG. 1.

[0031]FIG. 8 is a view of the FIG. 4 wafer fragment shown at aprocessing step subsequent to that of FIG. 6, and shown along an axiscorresponding to line X-X of FIG. 1.

[0032]FIG. 9 is a view of the FIG. 8 wafer fragment shown along an axiscorresponding to line Y-Y of FIG. 1.

[0033]FIG. 10 is a view of the FIG. 4 wafer fragment shown at aprocessing step subsequent to that of FIG. 8, and shown along an axiscorresponding to line X-X of FIG. 1.

[0034]FIG. 11 is a view of the FIG. 10 wafer fragment shown along anaxis corresponding to line Y-Y of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] This disclosure of the invention is submitted in furtherance ofthe constitutional purposes of the U.S. Patent Laws “to promote theprogress of science and useful arts” (Article 1, Section 8).

[0036] A method of forming a gated semiconductor assembly in accordancewith the present invention is described with reference to FIGS. 4-11.FIGS. 4, 6, 8 and 10 are views of a semiconductor wafer fragment shownat sequential steps of a fabrication process, and shown along an axiscorresponding to line X-X of FIG. 1. FIGS. 5, 7, 9 and 11 are views ofthe processed wafer fragments of FIGS. 4, 6, 8 and 10, respectively,along an axis corresponding to line Y-Y of FIG. 1.

[0037] Referring to FIGS. 4 and 5, a semiconductor wafer fragment 40comprises a substrate 42, and field oxide regions 44 formed oversubstrate 42. Substrate 42 and field oxide regions 44 can comprise thesame compositions as substrate 12 and field oxide regions 14 discussedabove in the “background” section. A portion of substrate 42 betweenfield oxide regions 44 is defined as an active region.

[0038] A first silicon dioxide layer 50 is formed over the activeregion. Silicon dioxide layer 50 can be formed by, for example, exposinga silicon-comprising substrate 42 to oxygen at temperatures of, forexample, at least 800° C.

[0039] A silicon-comprising floating gate layer 52 is formed over fieldoxide regions 44 and first silicon dioxide layer 50. Floating gate layer52 can comprise, for example, amorphous silicon or polycrystallinesilicon, and can be formed by, for example, chemical vapor deposition.The silicon of layer 52 is preferably doped with aconductivity-enhancing dopant to a concentration of greater than orequal to 1×10¹⁹ atoms/cm³. The dopant can be, for example, provided insitu during the chemical vapor deposition process, or provided byimplanting it into layer 52.

[0040] A silicon nitride layer 54 is formed over floating gate layer 52.In the shown preferred embodiment, silicon nitride layer 54 comprises afirst portion 56 and a second portion 58, with one of portions 56 and 58having a higher stoichiometric amount of silicon than the other ofportions 56 and 58. Preferably, upper portion 58 will have a greaterstoichiometric amount of silicon than will lower portion 56. Aninterface between portions 56 and 58 is illustrated with dashed line 57.In the shown embodiment, silicon nitride layer 54 is formed againstfloating gate layer 52. In other embodiments (not shown) an interveningsilicon oxide layer can be formed between silicon nitride layer 54 andfloating gate layer 52. Such intervening oxide layer can be formed by,for example, chemical vapor deposition or growth from the silicon offloating gate layer 52.

[0041] A preferred method of forming silicon nitride layer 54 is achemical vapor deposition process. A silicon precursor gas and anitrogen precursor gas are flowed into a reaction chamber at a firstratio to form portion 56 of silicon nitride layer 54, and then the ratiois changed to form portion 58. The silicon precursor gas can comprise,for example, SiH₂Cl₂ (dichlorosilane), and the nitrogen precursor gascan comprise, for example, NH₃ (ammonia). Example conditions fordepositing silicon nitride from NH₃ and SiH₂Cl₂ comprise temperatures offrom about 700° C. to about 800° C., and pressures of from about 100mTorr to about 1 Torr.

[0042] In a process wherein upper portion 58 is to have a greaterstoichiometric amount of silicon than lower portion 56, the initialratio of SiH₂Cl₂ to NH₃ flowed into a chemical vapor deposition can be,for example, about 0.33. Such ratio is flowed into the reaction chamberuntil first portion 56 is formed to a thickness of from about 50Angstroms to about 500 Angstroms, and preferably to a thickness of about75 Angstroms. The ratio of SiH₂Cl₂ to NH₃ of about 0.33 forms a firstportion 56 having a stoichiometry of about Si₃N₄.

[0043] After forming first portion 56, the ratio of SiH₂Cl₂ to NH₃ isadjusted to be greater than 0.33 (such as, for example, about 6) to formupper portion 58. Upper portion 58 is preferably formed to a thicknessof from about 50 Angstroms to about 500 Angstroms, preferably to athickness of less than or equal to about 200 Angstroms, and morepreferably to a thickness of less than or equal to about 100 Angstroms.Upper portion 58 preferably comprises a stoichiometry of Si_(x)N_(y),wherein a ratio of x to y is at least 1. For example, upper portion 58can comprise one or more of Si₄N₄, Si₇N₄ and Si₁₀N₁. If the ratio ofSiH₂Cl₂ to NH₃ is about 6, upper portion 58 will have a stoichiometry ofabout Si₄N₄.

[0044] Preferably, portions 56 and 58 are formed in a common anduninterrupted deposition process. By “common deposition process” it ismeant a deposition process wherein a wafer is not removed from areaction chamber between the time that an initial portion of a siliconnitride layer is formed and the time that a final portion of the siliconnitride layer is formed. By “uninterrupted deposition process” it ismeant a process wherein the flow of at least one of the siliconprecursor gas and the nitrogen precursor gas does not stop during thedeposition process.

[0045] In a most preferred embodiment of the invention, floating gatelayer 52 and silicon nitride layer 54 will be formed in a common anduninterrupted deposition process. Such uninterrupted deposition processcan comprise, for example, flowing SiH₂Cl₂ into a chemical reactionchamber, without NH₃ being flowed into the chamber, to deposit asilicon-comprising floating gate layer 52 over substrate 42. Floatinggate layer 52 is preferably formed to a thickness of from about 200Angstroms to about 2000 Angstroms. After formation of floating gatelayer 52, the SiH₂Cl₂ flow is maintained (although it may be reduced orincreased) and a flow of NH₃ is initiated in the chamber to form firstportion 56 of silicon nitride layer 54. The ratio of SiH₂Cl₂ to NH₃flowing within the reaction chamber is then altered to form secondportion 58 of silicon nitride layer 54.

[0046] After formation of silicon nitride layer 54, a patternedphotoresist layer 60 is formed over silicon nitride layer 54. Patternedphotoresist 60 is formed as follows. A photoresist material is providedover silicon nitride layer 54. The photoresist material is then exposedto a patterned beam of light to render portions of the material otherthan those of patterned layer 60 more soluble in a solvent than is thematerial of patterned layer 60. The solvent is then utilized to removethe more soluble portions and leave patterned layer 60.

[0047] Silicon nitride layer 54 can be utilized as an antireflectivelayer during exposure of the photoresist material to light.Specifically, it is observed that a refractive index of a siliconnitride layer increases as a stoichiometric amount of silicon increaseswithin the layer. For instance, it is observed that Si₄N₄ has a reactiveindex of 2.2, Si₇N₄ has a refractive index of 2.5, Si₁₀N₁ has arefractive index of 3.0, and Si₃N₄ has a refractive index of only 2.0. Amaterial is typically considered a suitable antireflective coatingmaterial if it has a refractive index of at least 2.2. Accordingly, theportions of silicon nitride layer 54 having a stoichiometry ofSi_(x)N_(y), where an x is at least equal to y, can be suitableantireflective materials.

[0048] Referring to FIGS. 6 and 7, a pattern from patterned photoresistlayer 60 (FIGS. 4 and 5) is transferred to layers 54 and 52 to patternlayers 54 and 56 into a floating gate stack 66. The pattern ofphotoresist layer 60 can be transferred to layers 52 and 54 by etchingportions of layers 52 and 54 which are not covered by photoresist layer60. A suitable etch can comprise, for example, a plasma-enhanced etchutilizing NF₃ and HBr.

[0049] Photoresist layer 60 (FIGS. 4 and 5) is removed from over siliconnitride layer 54. Subsequently, a layer of silicon dioxide 64 is grownover gate stack 66. Silicon dioxide layer 64 is formed along a sidewalland over a top surface of gate stack 66. Silicon dioxide layer 64 can beformed by, for example, growth from silicon of layers 52 and 54, or bychemical vapor deposition. Growth of silicon dioxide layer 64 can beaccomplished by exposing gate stack 66 to an atmosphere comprisingoxygen atoms at a temperature of at least about 500° C.

[0050] Referring to FIGS. 8 and 9, a control gate layer 74 is formedover gate stack 66 and substrate 42, and a patterned photoresist mask 76is formed over control gate layer 74. Control gate layer 74 cancomprise, for example, conductively doped amorphous silicon orpolycrystalline silicon, and can be formed by, for example, chemicalvapor deposition.

[0051] Referring to FIGS. 10 and 11, a pattern is transferred from mask76 (FIGS. 8 and 9) to control gate layer 74 to form layer 74 into acontrol gate over gate stack 66. The pattern can be transferred, with,for example, a plasma-enhanced etch utilizing NF₃ and HBr.

[0052] After formation of the control gate, an oxide layer 80 is formedover exposed surfaces of layers 52, 54 and 74. Oxide layer 80 can beformed by, for example, growth from the silicon of the control gate, orchemical vapor deposition.

[0053] Source and drain diffusion regions 72 are formed adjacent gatestack 66. Source and drain diffusion regions 72 can be formed by, forexample, implanting a conductivity-enhancing dopant into substrate 42.

[0054] If one or both of floating gate layer 52 and control gate layer74 comprise amorphous silicon, such layers are preferably converted topolycrystalline silicon in the gated semiconductor assembly of FIGS. 10and 11. Such conversion can occur by, for example, thermal processing ofthe layers at a temperature of at least about 700° C., and preferablyfrom about 700° C. to about 1100° C.

[0055] An advantage of the method of the present invention relative toprior art gated semiconductor assembly fabrication processes is that themethod of the present invention can utilize an insulative material layer(54) as an antireflective surface during photolithographic processing ofthe insulative layer. Accordingly, the method of the present inventioncan eliminate a prior art utilization of a separate antireflectivecoating layer during patterning of an insulative layer over a floatinggate construction. Another advantage of the method of the presentinvention is that it enables a common and uninterrupted depositionprocess to be utilized for formation of both a floating gate layer andan insulative layer over the floating gate layer.

[0056] As discussed above, it can be advantageous to have siliconnitride layer 54 comprise a portion having a stoichiometry ofSi_(x)N_(y), wherein x is greater than or equal to y, as such portioncan be utilized as an antireflective layer. It is noted that it can alsobe advantageous to have silicon nitride layer 54 comprise a portion witha stoichiometry of Si_(x)N_(y), wherein x is less than y, because suchportion can be easier to etch than a portion having a greaterstoichiometric amount of silicon. Accordingly, by having both types ofportions between silicon nitride layer 54, the layer can be utilized asan antireflective material, and yet can be relatively easily removedwhen patterned.

[0057] In compliance with the statute, the invention has been describedin language more or less specific as to structural and methodicalfeatures. It is to be understood, however, that the invention is notlimited to the specific features shown and described, since the meansherein disclosed comprise preferred forms of putting the invention intoeffect. The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A method of forming a gated semiconductor assembly, comprising:forming a silicon nitride layer over and contacting against a floatinggate; and forming a control gate over the silicon nitride layer.
 2. Themethod of claim 1 further comprising: forming a silicon dioxide layerover the silicon nitride layer; and forming the control gate over thesilicon dioxide layer.
 3. A method of forming a gated semiconductorassembly, comprising: forming a silicon nitride layer over a substrate,the silicon nitride layer comprising a first portion and a secondportion elevationally displaced from the first portion, the firstportion having less electrical resistance than the second portion; andforming a transistor gate over the silicon nitride layer.
 4. The methodof claim 3 further comprising: forming a floating gate layer over thesubstrate; and forming the silicon nitride layer over the floating gatelayer.
 5. The method of claim 3 further comprising: forming a floatinggate layer over the substrate; forming the silicon nitride layer overthe floating gate layer; and patterning the floating gate layer and thesilicon nitride layer into a floating gate shape.
 6. The method of claim3 wherein the second portion of the silicon nitride layer is over thefirst portion, the method further comprising: forming a silicon dioxidelayer over said second portion; and forming the control gate over thesilicon dioxide layer.
 7. The method of claim 6 wherein the forming thesilicon dioxide layer comprises growing the silicon dioxide from siliconof the second portion of the silicon nitride layer.
 8. The method ofclaim 3 wherein the silicon nitride layer comprises at least onesidewall, and wherein the second portion is over the first portion, themethod further comprising: forming a silicon dioxide layer over saidsecond portion and along the at least one sidewall of the siliconnitride layer; and forming the transistor gate over the silicon dioxidelayer.
 9. The method of claim 8 wherein the forming the silicon dioxidelayer comprises growing the silicon dioxide from silicon of the firstand second portions of the silicon nitride layer.
 10. The method ofclaim 3 wherein the forming the silicon nitride layer comprises:chemical vapor depositing the first portion utilizing a first mixturehaving a first ratio of a silicon precursor gas to a nitrogen precursorgas; and chemical vapor depositing the second portion utilizing a secondmixture having a second ratio of the silicon precursor gas to thenitrogen precursor gas, the first ratio being greater than the secondratio.
 11. The method of claim 10 wherein the chemical vapor depositingsof the first and second portions occur in a common and uninterrupteddeposition process.
 12. A method of forming a gated semiconductorassembly, comprising: forming a silicon nitride layer over a substrate,the silicon nitride layer comprising a first portion and a secondportion displaced from the first portion, the first portion having agreater stoichiometric amount of silicon than the second portion; andforming a gate over the silicon nitride layer.
 13. The method of claim12 further comprising incorporating the gate into one of an EPROM orEEPROM device as a control gate.
 14. A method of forming a gatedsemiconductor assembly, comprising: forming a silicon nitride layer overa substrate, the silicon nitride layer comprising a first portion and asecond portion elevationally displaced from the first portion, the firstportion having a greater stoichiometric amount of silicon than thesecond portion; and forming a transistor gate over the silicon nitridelayer.
 15. The method of claim 14 wherein the second portion of thesilicon nitride layer is over the first portion, the method furthercomprising: forming a silicon dioxide layer over said second portion;and forming the transistor gate over the silicon dioxide layer.
 16. Themethod of claim 15 wherein the forming the silicon dioxide layercomprises growing the silicon dioxide from silicon of the second portionof the silicon nitride layer.
 17. The method of claim 14 wherein thesilicon nitride layer comprises at least one sidewall, and wherein thesecond portion is over the first portion, the method further comprising:forming a silicon dioxide layer over said second portion and along theat least one sidewall of the silicon nitride layer; and forming thetransistor gate over the silicon dioxide layer.
 18. The method of claim17 wherein the forming the silicon dioxide layer comprises growing thesilicon dioxide from silicon of the first and second portions of thesilicon nitride layer.
 19. A method of forming a gated semiconductorassembly, comprising: forming a floating gate layer over a substrate;forming a silicon nitride layer over the floating gate layer, thesilicon nitride layer comprising a first portion and a second portionelevationally displaced from the first portion, the first portion havinga greater stoichiometric amount of silicon than the second portion; andforming a control gate over the silicon nitride layer.
 20. The method ofclaim 19 further comprising: forming a silicon dioxide layer over thesubstrate; and forming the floating gate layer over the silicon dioxidelayer.
 21. The method of claim 19 further comprising patterning thefloating gate layer into a floating gate shape after forming the siliconnitride layer.
 22. The method of claim 19 wherein the forming thesilicon nitride layer comprises: chemical vapor depositing the firstportion utilizing a first mixture having a first ratio of a siliconprecursor gas to a nitrogen precursor gas; and chemical vapor depositingthe second portion utilizing a second mixture having a second ratio ofthe silicon precursor gas to the nitrogen precursor gas, the first ratiobeing greater than the second ratio.
 23. The method of claim 22 whereinthe chemical vapor depositing the first portion occurs before thechemical vapor depositing the second portion.
 24. The method of claim 22wherein the chemical vapor depositing the first portion and the chemicalvapor depositing the second portion occur in a common and uninterrupteddeposition process.
 25. The method of claim 22 wherein the floating gatelayer comprises polycrystalline silicon.
 26. The method of claim 22wherein the forming the floating gate layer comprises: chemical vapordepositing amorphous silicon; and thermally treating the amorphoussilicon to form polycrystalline silicon.
 27. The method of claim 19wherein the floating gate layer comprises at least one of amorphoussilicon and polycrystalline silicon, and wherein the forming thefloating gate layer and the forming the silicon nitride layer occur in acommon and uninterrupted chemical vapor deposition process.
 28. Themethod of claim 19 further comprising: forming a silicon dioxide layerover the substrate; forming the floating gate layer over the silicondioxide layer, the floating gate layer comprising at least one ofamorphous silicon and polycrystalline silicon; forming the first portionof the silicon nitride layer by chemical vapor depositing utilizing afirst mixture having a first ratio of a silicon precursor gas to anitrogen precursor gas; and forming the second portion of the siliconnitride layer over the first portion by chemical vapor depositingutilizing a second mixture having a second ratio of the siliconprecursor gas to the nitrogen precursor gas, the first ratio beinggreater than the second ratio, the chemical vapor depositing the firstportion and the chemical vapor depositing the second portion occurringin a common and uninterrupted deposition process; after forming thefirst and second portions of the silicon nitride layer, forming apatterned photoresist layer over and against the second portion of thesilicon nitride layer; transferring a pattern from the patternedphotoresist layer to the polycrystalline silicon and the first andsecond portions of the silicon nitride layer to form a stack comprisingthe patterned floating gate layer and the patterned first and secondportions of the silicon nitride layer, the stack having at least onesidewall; growing a silicon dioxide layer over the second portion andalong the at least one sidewall of the stack; and forming the controlgate over the silicon dioxide layer.
 29. The method of claim 28 whereinthe patterned photoresist layer is formed against the silicon nitridelayer, wherein the patterned photoresist is formed by exposing aphotoresist material to light, and wherein the silicon nitride layer isutilized as an antireflective material during the exposure of thephotoresist material to light.
 30. A method of forming a semiconductorassembly, comprising: forming a first material layer over a substrate;forming a silicon nitride layer over the first material layer, thesilicon nitride layer comprising a first portion and a second portionelevationally displaced from the first portion, the first portion havinga greater stoichiometric amount of silicon than the second portion;forming a photoresist layer over the silicon nitride layer; patterningthe photoresist layer, the patterning comprising exposing portions ofthe layer of photoresist to light and utilizing the silicon nitridelayer as an antireflective material during the exposing; andtransferring the pattern from the patterned photoresist to the siliconnitride layer and the first material layer.
 31. The method of claim 30wherein the first material layer comprises at least one ofpolycrystalline silicon and amorphous silicon.
 32. The method of claim30 wherein the forming the silicon nitride layer comprises: chemicalvapor depositing the first portion utilizing a first mixture having afirst ratio of a silicon precursor gas to a nitrogen precursor gas; andchemical vapor depositing the second portion utilizing a second mixturehaving a second ratio of the silicon precursor gas to the nitrogenprecursor gas, the first ratio being greater than the second ratio. 33.The method of claim 32 wherein the chemical vapor depositing the firstportion and the chemical vapor depositing the second portion occur in acommon and uninterrupted deposition process.
 34. A gated semiconductorassembly, comprising: a silicon nitride layer over and contactingagainst a floating gate; and a control gate over the silicon nitridelayer.
 35. The gated semiconductor assembly of claim 34 furthercomprising a silicon dioxide layer between the silicon nitride layer andthe control gate.
 36. A gated semiconductor assembly, comprising: asilicon nitride layer over a substrate, the silicon nitride layercomprising a first portion and a second portion elevationally displacedfrom the first portion, the first portion having less electricalresistance than the second portion; and a gate over the silicon nitridelayer.
 37. The gated semiconductor of claim 36 wherein the gate is acontrol gate of an EPROM or an EEPROM device.
 38. The gatedsemiconductor of claim 36 further comprising: the second portion of thesilicon nitride layer being over the first portion; a silicon dioxidelayer over said second portion; and the control gate being over thesilicon dioxide layer.
 39. A gated semiconductor assembly comprising: asilicon nitride layer over a substrate, the silicon nitride layercomprising a first portion and a second portion elevationally displacedfrom the first portion, the first portion having a greaterstoichiometric amount of silicon than the second portion; and atransistor gate over the silicon nitride layer.
 40. The gatedsemiconductor of claim 39 further comprising: the second portion of thesilicon nitride layer being over the first portion; a silicon dioxidelayer over said second portion; and the transistor gate being over thesilicon dioxide layer.
 41. A gated semiconductor assembly comprising: asubstrate; a polycrystalline silicon layer over the substrate; a siliconnitride layer over the polycrystalline silicon layer, the siliconnitride layer comprising a first portion and a second portionelevationally displaced from the first portion, the first portion havinga greater stoichiometric amount of silicon than the second portion; anda control gate over the silicon nitride layer.
 42. The gatedsemiconductor of claim 41 wherein the first portion is over the secondportion.
 43. The gated semiconductor of claim 41 wherein the secondportion is over the first portion.
 44. A gated semiconductor assemblycomprising: a substrate; a floating gate over the substrate; a controlgate over the floating gate; and an electron barrier layer between thefloating gate and the control gate, the electron barrier layercomprising a silicon nitride layer, the silicon nitride layer comprisinga first portion and a second portion elevationally displaced from thefirst portion, the first portion having a greater stoichiometric amountof silicon than the second portion.
 45. The gated semiconductor of claim44 wherein the first portion is over the second portion.
 46. The gatedsemiconductor assembly of claim 44 wherein the electron barrier layerfurther comprises a silicon dioxide layer between the control gate andthe silicon nitride layer.
 47. The gated semiconductor assembly of claim44 wherein the floating gate comprises polycrystalline silicon and hasat least one sidewall, and wherein the silicon nitride layer has atleast one sidewall, the assembly further comprising a layer of dioxideextending along said sidewalls of the silicon nitride layer and thepolycrystalline silicon.